Method of producing hydrocarbon-expanded rigid polyurethane foams

ABSTRACT

A process for preparing polyurethane rigid foams from polyols and polyisocyanates as well as blowing agents and optionally foam auxiliary agents, characterized in that the polyurethane rigid foam is obtained by reacting 
     A) a polyol component with on average at least 3 hydrogen atoms, containing 
     1. 60 to 100% of polyethers and/or polyesters with at least 2 hydroxyl groups and a molecular weight of 250 to 1,500, which have a surface tension of 6 to 14 mN/m with respect to i-pentane and/or n-pentane as blowing agent, 
     2. i-pentane and/or n-pentane as blowing agent, 
     3. water and 
     4. optionally auxiliary agents and additives 
     with 
     B) a polyisocyanate with an NCO-content of 20 to 48 wt. % which has a surface tension of 4.0 to 8 mN/m with respect to i-pentane or n-pentane as blowing agent 
     is described.

BACKGROUND OF THE INVENTION

It is known that polyurethane rigid foams can be blown with low-boilingalkanes. Cyclic alkanes are used to advantage here because they make anoutstanding contribution to the thermal conductivity of the expandedmaterial due to their low gaseous thermal conductivity. Cyclopentane ispreferably used.

The beneficial properties when used as an insulator in domesticrefrigerators have to be compared with a disadvantageous commercialsituation. Thus, a specific quality of polystyrene inner container hasto be used, as a result of the solvent properties of cyclopentane.

Furthermore, cyclopentane has the disadvantage, due to its relativelyhigh boiling point of 49° C., that it condenses at low temperatures suchas are conventional during the use of polyurethane rigid foams asinsulators in domestic refrigerators. Due to the undesired condensationof the blowing agent, a reduced pressure is produced in the cells whichagain has to be offset by an elevated foam strength or increaseddensity.

Compared with the acyclic homologous pentane compounds, n-pentane andi-pentane, cyclopentane incurs higher manufacturing costs. n-pentane ori-pentane blown systems have been known for some time in the field ofpolyurethane rigid foams. However, the higher gaseous thermalconductivities, as compared with cyclopentane,which result in poorerthermal insulation capacity of the corresponding expanded systems is adisadvantage.

The object of the present invention was to develop a n-pentane ori-pentane blown rigid foam in which the disadvantages mentioned aboveare overcome and in particular in which low thermal conductivities areproduced.

Surprisingly, it has now been found that polyol formulations based onspecific polyethers and/or polyesters and polyisocyanates, which have aspecific surface tension with respect to n-pentane or i-pentane asblowing agent, produce expanded materials with particularly low thermalconductivities.

SUMMARY OF THE INVENTION

The invention provides a process for preparing polyurethane rigid foamsfrom polyols and polyisocyanates as well as blowing agents andoptionally foam auxiliary agents, characterised in that the polyurethanerigid foam is obtained by reacting

A) a polyol component with on average at least 3 hydrogen atoms,containing

1. 60 to 100% of polyethers and/or polyesters with at least 2 hydroxylgroups and a molecular weight of 250 to 1,500, which have a surfacetension of 6 to 14 mN/m with respect to i-pentane and/or n-pentane asblowing agent,

2. i-pentane and/or n-pentane as blowing agent,

3. water and

4. optionally auxiliary agents and additives

with

B) a polyisocyanate with an NCO-content of 20 to 48 wt. % which has asurface tension of 4.0 to 8 mN/m with respect to i-pentane or n-pentaneas blowing agent.

DETAILED DESCRIPTION OF THE INVENTION

Polyol formulations according to the invention preferably containpolyethers with a molecular weight of 250 to 1,500, obtained by thepolyaddition of 70 to 100 wt. % of ethylene oxide and 0 to 30 wt. % ofpropylene oxide to starter compounds.

Preferred compounds are sorbitol started polyethers with a molecularweight of 500 to 1,400 based on 70 to 100 wt. % of ethylene oxide and 0to 30 wt. % of 1,2-propylene oxide; sucrose started polyethers with amolecular weight of 500 to 1,400 based on 70 to 100 wt. % of ethyleneoxide and 0 to 30 wt. % of 1,2-propylene oxide; trimethylolpropanestarted polyethers with a molecular weight of 250 to 850 based on 70 to100 wt. % of ethylene oxide and 0 to 30 wt. % of 1,2-propylene oxide;glycerine started polyethers with a molecular weight of 250 to 850 basedon 70 to 100 wt. % of ethylene oxide and 0 to 30 wt. % of 1,2-propyleneoxide; o-toluylene-diamine started polyethers with a molecular weight of250 to 850 based on 70 to 100 wt. % of ethylene oxide and 0 to 30 wt. %of 1,2-propylene oxide.

According to the invention the polyol formulations preferably containpolyesters with a molecular weight of 200 to 600 formed from aromaticand aliphatic dicarboxylic acids and polyols containing at least 2hydroxyl groups. Examples of dicarboxylic acids are phthalic acid orphthalic anhydride, terephthalic acid, isophthalic aid, malonic acid andsuccinic acid. The following are preferably used as the alcoholcomponent for esterification: ethylene glycol, di, tri or tetraethyleneglycol or mixtures thereof.

Polyol formulations according to the invention may also containpolyether-esters, such as are obtainable by the reaction of phthalicanhydride with diethylene glycol and then with ethylene oxide (EP-A 0250 967).

Polyethers and polyesters according to the invention preferably have asurface tension of 6 to 14 mN/m, in particular 10 to 13, with respect ton-pentane and/or i-pentane.

In polyol formulations, these products are preferably present in aproportion of 60 to 100%, preferably 80 to 90%.

Polyisocyanates are preferably prepolymers with terminal NCO groups.

The isocyanate components are, e.g. aromatic polyisocyanates such as aredescribed, for instance, by W. Siefkin in Justus Liebigs Annalen derChemie, 562, pages 75 to 136, for example those of the formula

    Q(NCO).sub.n

in which

n is 2 to 4, preferably 2 and

Q represents an aliphatic hydrocarbon group with 2 to 18, preferably 6to 10, carbon atoms, a cycloaliphatic hydrocarbon group with 4 to 15,preferably 5 to 10, carbon atoms, an aromatic hydrocarbon group with 8to 15, preferably 8 to 13, carbon atoms, e.g. polyisocyanates like thosewhich are described in DE-OS 2 832 253, pages 10 to 11.

Industrially readily accessible polyisocyanates are generallyparticularly preferred, e.g. 2,4 and 2,6-toluylene diisocyanate and anymixture of these isomers ("TDI), polyphenylpolymethylene polyisocyanatessuch as can be prepared by aniline/formaldehyde condensation andsubsequent phosgenation (crude "MDI") and polyisocyanates withcarbodiimide groups, urethane groups, allophanate groups, isocyanurategroups, urea groups or biuret groups ("modified polyisocyanates"), inparticular modified polyisocyanates which are derived from 2,4 and2,6-toluylene diisocyanate or from 4,4' and/or 2,4'-diphenylmethanediisocyanate.

Starting components for the prepolymers are organic compounds with atleast one hydroxyl group.

Polyol or polyester components with a molecular weight of 60 to 1,400and containing 1 to 4 hydroxyl groups are preferred.

Polyesters with a molecular weight of 200 to 600 based on aromaticand/or aliphatic dicarboxylic acids and polyethers with a molecularweight of 60 to 1,400, obtained by the polyaddition of 70 to 100 wt. %of ethylene oxide and 0 to 30 wt. % of 1,2-propylene oxide to startercompounds such as ethylene glycol, trimethylolpropane and glycerine arepreferred.

Products produced from phthalic anhydride with diethylene glycol and/orethylene glycol are particularly preferred.

Polyether-esters with a molecular weight of 300 to 450, such as areobtainable by the reaction of phthalic anhydride with diethylene glycoland subsequently with ethylene oxide are also particularly preferred(EP-A 0 250 967).

Prepolymers according to the invention preferably have a surface tensionof 4.5 to 8 mN/m, in particular of 5 to 7 mN/m, with respect ton-pentane and/or i-pentane.

Paraffins or fatty alcohols or dimethylpolysiloxanes as well as pigmentsor colorants, also stabilisers against the effects of ageing andweathering, plasticisers and anti-fungal or anti-bacterial substances aswell as fillers such as barium sulphate, kieselguhr, carbon black orprepared chalk, may also be incorporated.

Further examples of optionally incorporated surface active additives andfoam stabilisers, as well as cell regulators, reaction retardants,stabilisers, flame inhibiting substances, colorants and fillers as wellas anti-fungal and anti-bacterial substances for use according to theinvention and details about the use and effects of these additives aredescribed in Kunststoff-Handbuch, vol. VII, published by Vieweg andHochtlen, Carl-Hanser-Verlag, Munich, 1966, e.g. on pages 121 to 205.

When preparing a foam, according to the invention the foaming proceduremay also be performed in closed moulds. In this case the reactionmixture is introduced into a mould. Suitable mould materials are metals,e.g. aluminium, or plastics, e.g. epoxide resin. The foamable reactionmixture foams in the mould and forms the moulded item. The mould-foamingprocedure may be performed in such a way that the moulded item has acellular structure at its surface. It may also be performed, however, insuch a way that the moulded item has a solid skin and a cellular core.According to the invention, the procedure in the first case is tointroduce sufficient foamable reaction mixture into the mould for thefoam produced to just fill the mould. The mode of operation in thelast-mentioned case comprises introducing more foamable reaction mixtureinto the mould than is required to fill the interior of the mould withfoam. In the latter case, therefore, the process uses "overcharging", atype of procedure which is known, e.g. from U.S. Pat. Nos. 3,178,490 and3,182,104.

The invention also provides use of the rigid foam prepared according tothe invention as an intermediate layer for laminated elements and forfilling the hollow spaces in domestic refrigerators with foam.

The process according to the invention is preferably used for fillingthe hollow cavities in refrigerator and freezer housings with foam.

Obviously, expanded materials may also be produced by block foaming orby the double transport method which is known per se.

The rigid foams obtainable according to the invention are used, forinstance, in the building industry and for the insulation oflong-distance energy pipes and containers.

The following examples are intended to explain the invention without,however, restricting its scope.

The surface tension was determined by the conditions in appendix V ofthe Directive described in the Official Journal of the EuropeanCommunity in accordance with Directive 92/69/EWG (17th amendment toDirective 67/548/EWG) with the OECD ring method, taking the GLP intoaccount.

EXAMPLE 1 (COMPARISON EXAMPLE)

Formulation for Polyurethane Rigid Foam

Component A

50 parts by wt. sucrose (80 wt. %) and propylene glycol (20 wt. %)started polyether with a molecular weight of 600, obtained by anionicpolyaddition using 1,2-propylene oxide (surface tension with respect ton-pentane: 4.4 mN/m)

25 parts by wt. trimethylolpropane started polyether with a molecularweight of 430, obtained by anionic polyaddition using 1,2-propyleneoxide (surface tension with respect to n-pentane: 1.3 mN/m)

25 parts by wt. propylene glycol started polyether with a molecularweight of 1,000, obtained by anionic polyaddition using 1,2-propyleneoxide (surface tension with respect to n-pentane: 0.8 mN/m)

2.5 parts by wt. water

2.0 parts by wt. foam stabiliser, B 8423 (from Goldschmidt)

2.0 parts by wt. activator, Desmorapid 726b (Bayer AG)

Component B

125 parts by wt. crude MDI (NCO content=31.5 wt. %) (surface tensionwith respect to n-pentane 3.3 mN/m)

100 parts by wt. of component A were mixed with 11 parts by wt. ofn-pentane and 125 parts by wt. of component B using a stirrer (2,000rpm) at 20° C. and compressed in a closed mould at 34 kg/m³.

EXAMPLE 2 (COMPARISON EXAMPLE)

Formulation for Polyurethane Rigid Foam

Component A

100 parts by wt. sorbitol started polyether with a molecular weight of640, obtained by anionic polyaddition using ethylene oxide (surfacetension with respect to n-pentane: 12.4 mN/m)

2.5 parts by wt. water

2.0 parts by wt. foam stabiliser, B 8423 (from Goldschmidt)

2.0 parts by wt. activator, Desmorapid 726b (Bayer AG)

Component B

168 parts by wt. crude MDI (NCO content=31.5 wt. %) (surface tensionwith respect to n-pentane 3.3 mN/m)

100 parts by wt. of component A were mixed with 11 parts by wt. ofn-pentane and 168 parts by wt. of component B using a stirrer (2,000rpm) at 20° C. An expanded material could not be obtained due to thestructure collapsing.

EXAMPLE 3 (COMPARISON EXAMPLE)

Formulation for Polyurethane Rigid Foam

Component A

50 parts by wt. sucrose (80 wt. %) and propylene glycol (20 wt. %)started polyether with a molecular weight of 600, obtained by anionicpolyaddition using 1,2-propylene oxide (surface tension with respect ton-pentane: 4.4 mN/m)

25 parts by wt. trimethylolpropane started polyether with a molecularweight of 430, obtained by anionic polyaddition using 1,2-propyleneoxide (surface tension with respect to n-pentane: 1.3 mN/m)

25 parts by wt. propylene glycol started polyether with a molecularweight of 1,000, obtained by anionic polyaddition using 1,2-propyleneoxide (surface tension with respect to n-pentane: 0.8 mN/m)

2.5 parts by wt. water

2.0 parts by wt. foam stabiliser, B 8423 (from Goldschmidt)

2.0 parts by wt. activator, Desmorapid 726b (Bayer AG)

Component B

146 parts by wt. prepolymer with an NCO content of 27 wt. %, obtained byreacting 92 wt. % of crude MDI (NCO content=31.5 wt. %) with 8 wt. % ofpolyether-ester with a molecular weight of 370 based on phthalicanhydride, diethylene glycol and ethylene oxide.

100 parts by wt. of component A were mixed with 11 parts by wt. ofn-pentane and 146 parts by wt. of component B using a stirrer (2,000rpm) at 20° C. and compressed in a closed mould at 34 kg/m³.

EXAMPLE 4 (ACCORDING TO THE INVENTION)

Formulation for Polyurethane Rigid Foam

Component A

100 parts by wt. sorbitol started polyether with a molecular weight of640, obtained by anionic polyaddition using ethylene oxide (surfacetension with respect to n-pentane: 12.4 mN/m)

2.5 parts by wt. water

2.0 parts by wt. foam stabiliser, B 8423 (from Goldschmidt)

2.0 parts by wt. activator, Desmorapid 726b (Bayer AG)

Component B

196 parts by wt. prepolymer with an NCO content of 27 wt. %, obtained byreacting 92 wt. % of crude MDI (NCO content=31.5 wt. %) with 8 wt. % ofpolyether-ester with a molecular weight of 370 based on phthalicanhydride, diethylene glycol and ethylene oxide (surface tension withrespect to n-pentane 5 mN/m)

100 parts by wt. of component A were mixed with 11 parts by wt. ofn-pentane and 196 parts by wt. of component B using a stirrer (2,000rpm) at 20° C. and compressed in a closed mould at 34 kg/m³.

EXAMPLE 5 (ACCORDING TO THE INVENTION)

Component A

80 parts by wt. sorbitol started polyether with a molecular weight of640, obtained by anionic polyaddition using ethylene oxide (surfacetension with respect to n-pentane: 12.4 mN/m)

20 parts by wt. polyether-ester with a molecular weight of 370 based onphthalic anhydride, diethylene glycol and ethylene oxide (surfacetension with respect to n-pentane: 12.3 mN/m)

2.5 parts by wt. water

2.0 parts by wt. foam stabiliser, B 8423 (from Goldschmidt)

2.0 parts by wt. activator, Desmorapid 726b (Bayer AG)

Component B

193 parts by wt. prepolymer with an NCO content of 25.5 wt. %, obtainedby reacting 90 wt. % of crude MDI (NCO content=31.5 wt. %) with 10 wt. %of polyether-ester with a molecular weight of 355 based on phthalicanhydride and diethylene glycol (surface tension with respect ton-pentane 6.4 mN/m)

100 parts by wt. of component A were mixed with 11 parts by wt. ofn-pentane and 193 parts by wt. of component B using a stirrer (2,000rpm) at 20° C. and compressed in a closed mould at 34 kg/m³.

The test figures in the following Table were obtained for the foamsheets prepared in examples 1 to 5.

    ______________________________________                                                    Thermal conductivity                                                          [mW/mK] according to                                              Example     DIN 52616, 24° C.                                          ______________________________________                                        1           24                                                                2           collapsed                                                         3           23.3                                                              4           20.5                                                              5           20.0                                                              ______________________________________                                    

As can be seen from examples 4 and 5, n-pentane blown PUR rigid foamswith much lower thermal conductivities can be obtained by combiningpolyethers and polyisocyanates according to the invention.

We claim:
 1. A process for preparing polyurethane rigid foams frompolyols and polyisocyanates as well as blowing agents and optionallyfoam auxiliary agents, characterised in that the polyurethane rigid foamis obtained by reactingA) a polyol component with on average at least 3hydrogen atoms, containing1. 60 to 100% of polyethers and/or polyesterswith at least 2 hydroxyl groups and a molecular weight of 250 to 1,500,which have a surface tension of 6 to 14 mN/m with respect to i-pentaneand/or n-pentane as blowing agent, wherein the polyethers are obtainedby the polyaddition of 70 to 100 wt. % of ethylene oxide and 0 to 30 wt.% of propylene oxide to starter compounds
 2. i-pentane and/or n-pentaneas blowing agent,
 3. water and
 4. optionally auxiliary agents andadditiveswith B) a polyisocyanate with an NCO-content of 20 to 48 wt. %which has a surface tension of 4.0 to 8 mN/m with respect to i-pentaneor n-pentane as blowing agent.
 2. A process for preparing polyurethanerigid foams according to claim 1, characterised in that a sorbitolstarted polyether with a molecular weight of 500 to 1,400 based on 70 to100 wt. % of ethylene oxide and 0 to 30 wt. % of 1,2-propylene oxide isused.
 3. A process for preparing polyurethane rigid foams according toclaim 1, characterised in that a sucrose started polyether with amolecular weight of 500 to 1,400 based on 70 to 100 wt. % of ethyleneoxide and 0 to 30 wt. % of 1,2-propylene oxide is used.
 4. A process forpreparing polyurethane rigid foams according to claim 1, characterisedin that a trimethylolpropane started polyether with a molecular weightof 250 to 850 based on 70 to 100 wt. % of ethylene oxide and 0 to 30 wt.% of 1,2-propylene oxide is used.
 5. A process for preparingpolyurethane rigid foams according to claim 1, characterised in that aglycerine started polyether with a molecular weight of 250 to 850 basedon 70 to 100 wt. % of ethylene oxide and 0 to 30 wt. % of 1,2-propyleneoxide is used.
 6. A process for preparing polyurethane rigid foamsaccording to claim 1, characterised in that an o-toluylene diaminestarted polyether with a molecular weight of 250 to 850 based on 70 to100 wt. % of ethylene oxide and 0 to 30 wt. % of 1,2-propylene oxide isused.
 7. A process for preparing polyurethane rigid foams according toclaim 1, characterised in that a polyester with a molecular weight of200 to 600, formed from aromatic and aliphatic dicarboxylic acids andpolyols with at least 2 hydroxyl groups, is used.
 8. A process forpreparing polyurethane rigid foams according to claim 1, characterisedin that a prepolymer with an NCO content of 20 to 33 wt. % and withterminal NCO groups, which has been obtained by reacting1.4,4'-diphenylmethane diisocyanate, optionally in a mixture with the 2,4and 2,2-isomers and 0 to 30 wt. % of higher functional fractions, with2. a polyether with a molecular weight of 60 to 1,400 obtained by thepolyaddition of 70 to 100 wt. % of ethylene oxide and 0 to 30 wt. % of1,2-propylene oxide,is used as the polyisocyanate.
 9. A process forpreparing polyurethane rigid foams according to claim 1, characterisedin that a prepolymer with an NCO content of 20 to 33 wt. % and withterminal NCO groups, which has been obtained by reacting1.4,4'-diphenylmethane diisocyanate, optionally in a mixture with the 2,4and 2,2-isomers and 0 to 30 wt. % of higher functional fractions, with2. a polyester with a molecular weight of 200 to 600 based on aromaticand aliphatic dicarboxylic acids and polyols with at least 2 hydroxylgroups,is used as the polyisocyanate.
 10. A process for preparingpolyurethane rigid foams according to claim 1, characterised in that aprepolymer with an NCO content of 25 to 45 wt. % and with terminal NCOgroups which has been obtained by reacting1. toluylene diisocyanate,optionally a mixture of the 2,4 and 2,6-isomers and 0 to 30 wt. % ofhigher functional fractions, with
 2. a polyether with a molecular weightof 60 to 1,400 obtained by the polyaddition of 70 to 100 wt. % ofethylene oxide and 0 to 30 wt. % of 1,2-propylene oxide to startercompounds,is used as the polyisocyanate.
 11. A process for preparingpolyurethane rigid foams according to claim 1, characterised in that aprepolymer with an NCO content of 25 to 45 wt. % and with terminal NCOgroups, which has been obtained by reacting1. toluylene diisocyanate,optionally a mixture of the 2,4 and 2,6-isomers and 0 to 30 wt. % ofhigher functional fractions, with
 2. a polyester with a molecular weightof 200 to 600 based on aromatic and aliphatic dicarboxylic acids andpolyols with at least 2 hydroxyl groups,is used as the polyisocyanate.